I would recommend investing 100% in a better headphone amp. For the money you are talking you need to put it all in the amp. While, like main systems, all the components matter. I find that headphone amps really matter. The most important changes have come for me through the headphone amp. I recommend Woo Headphone amps.
I own half a dozen top tier headphones and have owned at least a dozen headphone amps. I never really got going until I discovered Woo. Natural, and powerful (depending on the model). Great company as well. Read, call them up and discuss.